1. Field of the Invention
This invention relates to door closing mechanisms and in particular to devices to allow doors to close automatically in the case of fire, etc.
2. Prior Art
In many public buildings, such as hospitals, it is common practice to use spring operated door closing mechanisms on all fire doors which operate to hold the doors in a normal open position but which are automatically operated by various types of sensing devices to close the doors in the event of fire. Most such devices use a normally energized electromagnet which renders the door closer inoperative when the door is in the open position and which are energized by fire sensing devices in the presence of smoke, fire, etc., to release the door closing mechanism so that the doors will close.
In most mechanisms of this nature, components of the mechanism for obtaining automatic release of the doors are incorporated in the spring closure mechanisms so that if such doors have initially been provided with spring operated door closers only, it is necessary to remove the entire spring closer unit and replace it with the automatic closer device. Conversion to automatically operated devices for all the doors of a building in which the doors have not been so equipped is therefore very costly.